This invention generally relates to processes for the preparation of resin compositions, and more specifically, the present invention is directed to a bead polymerization process for affecting preparation of toner resin compositions. In one embodiment the present invention is directed to an aqueous bead suspension polymerization process for obtaining in an efficient manner resin particles having a low molecular weight wax component therein, or grafted thereon, which resin particles subsequent to further processing can be formulated into toner compositions. The toner compositions formulated in accordance with the process of the present invention are useful in permitting the development of images in electrostatic imaging systems wherein an offset preventing liquid such as a silicone oil is not required.
Numerous methods are known for preparing toner resin compositions, including processes for generating these compositions with waxes therein. There is thus described for example in British Pat. No. 1,442,835, standard melt mixing methods for obtaining a toner composition containing a styrene homopolymer or copolymer resin, and at least one polyalkylene compound of an average molecular weight of from about 2,000 to about 6,000 and selected from polyethylene and polypropylene. According to the disclosure of this patent reference page 2 beginning at line 90, the starting polymer resin may be either a homopolymer of styrene, or a copolymer or styrene with other ethylenically unsaturated monomers, specific examples of which are disclosed on page 3 beginning at line 1.
Additionally, there is disclosed in a copending application U.S. Ser. No. 434,198/82, entitled Positively Charged Toner Compositions, several methods, including dispersion polymerization, melt blending, and spray drying processes for generating a developer composition mixture comprised of electrostatic toner particles consisting of resin particles, pigment particles, and a waxy material with a molecular weight of from about 500 to about 20,000. Also there can be included in the aforementioned composition from about 0.5 percent by weight to about 10 percent by weight of a charge enhancing additive selected from, for example, alkyl pyridinium halides, organic sulfonate compositions, and organic sulfate compositions. The disclosure of this copending application is totally incorporated herein by reference.
Further, there is disclosed in U.S. Pat. No. 4,148,741, a specific method for the formulation of toner compositions by bead polymerization processes. More specifically there is disclosed in this patent a process for obtaining toner particles by a method which involves dispersing in an aqueous medium a monomer having dispersed therein a pigment. Thereafter, the pigmented monomer is formed into droplets of a particle size of from 200 to about 600 microns, and the resulting particles are polymerized, permitting the formation of polymerized beads. Subsequent to separation of the beads from the water solution they are attrited, and there results toner particles which may be combined with suitable carrier compositions to generate electrostatic developer compositions.
There are further disclosed in the '741 patent several other methods for the preparation of toner compositions, reference column 2 line 14 to column 4, line 32. These methods involve for example the mixing of a softened resin and pigment followed by blending these components in a rubber mill and pulverizing; blending a water latex of the desired toner resin with a colorant, and thereafter spray drying these components to the desired particle size; emulsion polymerization directly from a monomer by polymerization thereof by, for example, preparing a kneaded oil phase component with one or more liquid resin monomers, coloring material, polymerization inhibitor, a finely divided inorganic stablizer, and a polar resinous additive which is soluble in the monomer; and suspension polymerization processes wherein an inorganic stabilizer is not used in the reaction and there results encapsulated toner compositions.
Disclosed in U.S. Pat. No. 3,997,488 is a multistep process for the provision of dispersions with a graft copolymer, and at least one substance selected from the group consisting of wax, or polyethylene in an organic solvent. More specifically, the process disclosed in this patent involves affecting the four steps as outlined in column 1, line 45. This process is accomplished in the presence of organic solvent, while in contrast the invention of the present application is affected in an aqueous medium thereby avoiding the problems associated with removal of the solvent from the reaction mixture, and contamination.
Also, there is disclosed in U.S. Pat. No. 4,206,247, a developer composition containing a mixture of resins including a low molecular weight polyolefin and alkyl modified phenol resins. More specifically it is indicated in this patent, reference column 4, line 6, that the invention is directed to a process which comprises the steps of developing an image with toner particles containing in certain proportions at least one resin selected from group A, and at least one resin selected from group B resins, wherein the resins of group A include a low molecular weight polyethylene, a low molecular weight polypropylene, and similar materials; and wherein the group B resins include natural resin modified maleic acid resins, natural modified pentaerythritol resins, and other resins. As examples of group A resins there are mentioned polystyrene, styrene series copolymers, polyesters, epoxy resins, and the like, reference the disclosure in column 5, line 47. The molecular weight of the polypropylene, or polyethylene used is from about 1,000 to about 10,000, and preferably from about 1,000 to about 5,000. These compositions are prepared by the known melt blending processes as described hereinbefore.
While the above described processes are suitable for their intended purposes there remains a need for other processes for affecting the preparation of resin particles, and toner compositions. Additionally, there remains a need for the preparation of resin particles containing waxes therein, or grafted thereon by a bead suspension polymerization wherein the reaction is accomplished in the absence of solvents. There also is a need for accomplishing the preparation of toner resin particles in an economical and efficient manner and wherein the bead suspension method selected enables the use of aqueous solutions, thus enabling toner compositions to be prepared without extensive processing. Moreover, there remains a need for bead suspension polymerization processes for preparing toner and developer compositions having incorporated therein low molecular weight waxes functioning as release materials, for example, allowing such compositions to be used for the development and fixing of electrostatic latent images where an offset preventing liquids, such as silicone oils are not required. In order to substantially eliminate offsetting, and more specifically for the purpose of preventing adhesion of the toner particles to the surface of the fixing roller, there has been selected certain types of rollers the surface of which may be covered with a thin film of an offset preventing liquid such as a silicone oil. These oils are highly effective, however, the apparatus within which they are incorporated is complicated and costly since, for example, a means for feeding the oil is required. Also, not only do the silicone oils emit an undesirable odor, these oils deposit on the machine components causing toner particles to collect on, and adhere to the silicone oils, which is highly undesirable. An accumulation of toner particles on machine components is troublesome in that the image quality is affected, and these components must be periodically cleaned and/or replaced, adding to the maintenance costs of the machine system involved.